JOURNAL OF CONCHOLOGY. 4x5 



ON DREISSENSIA POLYMORPHA Pallas. 



By Prof. Dr. E. v. MARTENS. 



(Read before the Conchological Society, Aug. 22nd, 1894). 



To the question brought forward in the last number of the 

 'Journal of Conchology,' (page 404), concerning Dreissensia 

 polymorpha or volgensis, I may be allowed to answer that 

 Pallas's voyage in Southern Russia and Siberia, on which he 

 detected this shell, was in the years 1 768-1 770. He found the 

 said shell at the mouth of the Jaik or Ural river, in August, 

 1769, and the first volume of his work on his voyage in which 

 this shell is described, was published in 1771 ; an abbreviated 

 German edition, published in 1776, is now before me, in which 

 at page 26 of the appendix the description of Mytilus poly- 

 morphus is given in full. Further, the name and description is 

 given also in Schroter's 'A Geschichte dor Flussconchylien,' 

 1779, page 197. It is therefore a mistake to surmise that the 

 name Mytilus polymorphus was given before 1758, and should 

 yield to M. volgensis Chemn., all the said publications being 

 between 1758 and 1795, the date of Chemnitz's '■Mytilus e fluvio 

 PVolga' (not '■volgensis'') in the xi. volume of his ' Conchylien 

 Cabinet/ page 256. 



Neither is the circumstance that Pallas has distinguished a 

 M. polyjnorphus marinus and fluviatilis of any value for the 

 rejection of the name. Pallas states in the description of his 

 voyage that he did find some of his shells in the river Jaik itself, 

 and others in a living state on the shore of the island Kamenoi, 

 at the mouth of this river in the Caspian Sea. Those from the 

 river were of larger size and angulated, those from that island 

 smaller and not so sharply angulated ; but, nevertheless ' prse- 

 sertim versus nates carinata.' With regard to the size, he 



